This invention relates to internal combustion (I.C.) engines and more specifically to a novel method for fabricating components of such engines by plastic molding. The invention eliminates flash at the intersection of passages within the components, wherein the intersecting passages are formed by different core pins inserted into the molding cavity. The invention will be described with reference to the molding of fuel passages in a molded plastic fuel rail.
In the practice of molding I.C. fuel rails from plastic, fuel passages are formed in the molded part by disposing core pins in the mold cavity and molding the part around these core pins. Where passages intersect, there is a separate core pin for each intersecting passage, and it has been the practice to abut the end of one core pin with the side of another at each point of intersection. When plastic is injected under high pressure into the mold cavity, it can intrude between the abutting and abutted core pins and create a residual thin film, or flash, at the intersection of two fuel passages. Such flash can impair the fuel flow from one passage to the other. Where fuel is introduced into the engine's air/fuel system by means of an electromagnetic fuel injector, flash in a fuel path feeding the injector can have a negative effect on accuracy of fuel injection. It is therefore necessary to remove such flash by secondary operations in order to make the molded part commercially suitable. Unfortunately, the need for secondary operations adds to the manufacturing cost. Also, if the material comprising the flash separates from the main fuel rail, then it can become lodged in some other part of the fuel system, e.g. an injector or regulator.
Even if an attempt is made to solve the problem by providing a close fitting abutment of the end of one core pin with the side of another core pin, significant axial force must be imparted to the one core pin, and this will give rise to core pin deflection that defeats the close fit so that flash is likely to be formed in any event. Repeated cycling of a mold also results in core pin wear that amplifies the flash problem over the course of a production run. This flash problem is a serious impediment to the successful commercial development of mass-produced molded plastic fuel rails.
The present invention relates to a novel method for making molded plastic fuel rails that solves this flash problem. Instead of merely forcefully abutting the end of one core pin with the side of another, the solution that is disclosed by the present invention involves providing a threaded projection at the end of the abutting core pin and a complementary threaded recess in the side of the abutted core pin, and tightly threading the end of the abutting core pin into the threaded recess in the side of the abutted core pin to thereby form a seal between the two. This screw thread connection greatly increases the magnitude of force by which a shoulder on the abutting core pin can be urged against the abutted core pin so that as a consequence, a highly effective seal is attained by the abutment of this shoulder with the side of the abutted core pin. The creation of flash at the intersection of two fuel passages is thereby essentially eliminated. After the fuel rail has been molded, the threaded connections are unthreaded and the core pins are withdrawn, thereby allowing the molded part to be removed from the mold cavity. The present invention is a significant step in making molded plastic fuel rails feasible for commercial mass production.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.